This invention relates to normally sealed lead-acid cells of the oxygen recombination type, and more particularly to an integrated plate/separator configuration and the associated method for its production.
Sealed lead-acid batteries of one or more cells operating on the oxygen cycle with internal recombination of oxygen during charge and reasonable overcharge are taught in U.S. Pat. No. 3,862,861 to McClelland et al. These starved electrolyte batteries exhibit unique performance in part by employing an absorptive separator mat preferably of microfine glass fibers having a large surface area per unit of volume and a large porosity, enabling retention of the bulk of the acid electrolyte (capacity determining) of the cell in the separator phase, while leaving a sufficiently thin layer of electrolyte on the active plate surface to sustain internal oxygen recombination within the cell at high efficiencies.
In commercial practice, electrode plates for these cells have been produced by continuously pasting a lead grid with electrochemically active paste material. After the pasted grid exits a pasting nozzle, a cellulosic paper has been applied to the paste to aid in paste spreading, to keep moisture in the plate prior to drying, and to keep the paste contained prior to winding or stacking the plates and interleaved glass mat separator to form a cell pack subassembly. Typically, due to interference of the cellulosic paper with cell/battery performance characteristics, it is removed and discarded prior to assembly. This so-called pasting paper is a nuisance because of its cost, the necessity for proper disposal, and because roughly 2 to 4% of the paste is removed with the paper as it is stripped off the pasted plate. In addition, paper stripping and plate scraping contributes substantially to undesirably high airborne lead dust levels. Representative prior art that discloses the use of such disposable pasting paper and typical pasting methods for sealed lead-acid batteries include U.S. Pat. Nos. 3,814,628 and 3,881,654 to Larkin, 3,894,886 to Pankow et al, 4,050,482 to Ching et al, and 4,318,430 to Perman.
In another prior art method the pasting paper, typically cellulosic, remains on the plates during winding/stacking and subsequent battery assembly, and this paper degrades within the battery during electrochemical formation and subsequent use.
U.S. Pat. No. 4,429,442 to Thomas discloses a method of producing a lead-acid battery plate by supplying active paste to a carrier, contacting the exposed surface of the paste on the carrier with a layer of fibrous material such as glass fiber mat or a randomly oriented, woven or knitted synthetic resin fabric such as polyester, and supplying vibrational energy to the fibrous layer so as to cause the paste to impregnate the fibrous layer and thereby secure the fibrous layer to the plate.
Japanese Patent Appl. No. 55-14133 (Publication No. 56-112070) to Okamoto et al teaches a plate manufacturing method for an enclosed lead battery including the steps of coating a soft lead or lead alloy support with an active paste substance having a high moisture content, sandwiching the pasted plate between acid-resistant porous separator layers made, for example, of a nonwoven glass fiber, and then passing the pasted plate with separator layers through a pair of press rollers, which are provided on their surface with liquid absorbant cloth that absorbs moisture from the separator layers. The plate/separator subassembly may be coiled to form a spiral wound cell.
Reference is also made to U.S. Pat. No. 4,469,145 to Fletcher et al, which discloses use of glass fiber tissues applied on either side of a pasted negative grid to retain the paste in position.
U.S. Pat. No. 4,414,295 to Uba discloses a sealed lead-acid battery using a multilayer microfine glass separator in which the layers positioned against the plates have a relatively high surface area, and a sandwiched glass layer has a relatively low surface area.
It is a primary object of the subject invention to provide a separator pasting paper for sealed lead-acid cells that remains on the plates and is incorporated into the finished cell, thereby avoiding the traditional paper stripping and plate scraping steps associated with disposable pasting papers, to reduce airborne lead dust levels during plate preparation, and to provide a unique separator pasting separator material, which intimately integrates with the adjoining pasted plate, thereby improving ionic transfer during use of the battery, and its high rate performance.